This invention relates in general to intravascular catheters and more particularly to a catheter that is inserted into and through blood vessels for the purpose of injecting radiopaque substances to aid in the imaging of blood vessels and organs. Such catheters are called angiographic catheters.
It is known to incorporate a soft tip in the leading or distal end of these catheters to avoid injury to the walls of the blood vessels. The body of the catheter, however, has to be relatively stiff to withstand the pressure of the radiopaque material being delivered through the catheter and to provide enough torqueability so that the tip, usually curved, can be directed through the blood vessel.
A known type of soft tip catheter is disclosed in U.S. Pat. No. 4,563,181 issued on Jan. 7, 1989 to Wijayarathna and Hopkins. The patent provides a useful description of the prior art and of the need for the combination of a soft tip portion and a stiff body portion. To properly locate the catheter in the patient, it is important that the distal end of the catheter be sufficiently radiopaque so as to make it readily visible on the fluoroscopy screen.
Polymer materials and in particular nylons of great structural strength have become available which make it possible to design very thin wall catheters to withstand high pressure without bursting. Pressures of up to 1,200 psi have to be withstood by the catheters in use. Because of these very thin wall sections, it is now possible, to produce a 5 French catheter with inside diameters that exceed the inside diameters of old style 6 French catheters. However, these extremely thin wall catheters, which can be in the range of 8 to 11 mils (0.008 to 0.010 inches) in wall thickness, provide such small sidewall thickness that it is difficult to view and guide the catheter under fluoroscopy.
Accordingly, a purpose of this invention is to provide a soft tip and relatively stiffer body angiographic catheter with enhanced visibility under fluoroscopy.
Because of the thin sidewall and the high pressures, it is important that the soft material of the tip bond with sufficient strength to the flexible, though relatively stiff material of the body to avoid detaching the tip under internal catheter pressure.
Accordingly, it is another purpose of this invention to provide a highly radiopaque tip which has a high bonding strength to the catheter body.
From the point of view of tissue trauma and damage, it is useful to have as small an outside diameter (O. D.) catheter as possible. Since the inside diameter is essentially dictated by the amount and rate of liquid that has to be injected, the thinner the wall, the smaller the O. D.
Accordingly, there is a trade-off between small wall thickness, high burst strength and visibility under fluoroscopy. It is a significant object of this invention to provide a soft tip angiographic catheter design which provides an enhanced trade-off of these parameters.